Clasping the handstogether palm-to-palm, insert wet (preferably brined) hands in the anus of partner, and proceed to open and close the hands as if they are a clam, using the wrists as a hinge of sorts.
Clifford’s female companion smelled of fish, so in the spirit of the sea, he hand clammed that ass until he got a brown pearl.
Phrase: The act of placing one's fist into the vaginal cavity of said women while she is squatting. Then elevating woman off of her feet to put her on display for other enjoyment.
Guy 1: Dude did you see Arnold and that bitch in a one hand clam stand last night?
Guy 2: Yeah, It made for a good show with all the noise.